The field of orthopedic medicine has grown tremendously in the past fifty years as surgical techniques, implants and instrumentation have developed and been improved. The small bones are frequently subject to the need for re-constructive surgery for example, as a result of trauma, to counteract the effects of aging or to repair congenital deformities and trauma and spinal areas. While there is a wide variety in the exact shape and mass of all bones, these variations become more problematic in providing orthopedic implants for small bone applications since there is less room on and about the bone for the surgeon to place and fix the construct. These bones are finer and have less surface area for placement of an implant, and less mass for the placement of screws and as a result, individual variations become more problematic for orthopedic plates of stock design. Consequently, surgeons have tended to rely on the use of screws and wires for reconstruction or have had to resort to operating room contouring procedures which can weaken the plates and/or distort the screw holes within the plates. This is a particular problem in instances in which either variable locking mechanisms are used, or in which locking screws are used with the plates. None-the-less, locking screws often are used to advantage as they provide more secure placement of the screws in the bone, cause better compression through a fractures, and can be less likely to harm the bone or back out of the plate.
One problem that needs to be avoided in the delicate environment of the small bone area is the interference of screws, with other screws, and with the function of ligaments and tendons. While it may be desirable to design an orthopedic plate so that securing screws converge in order to cause compression or increase the pullout strength, it is difficult when a screw impinges on or conflicts with the desired placement of another screw. Some surgeons prefer bicortical fixation in which a screw is sized so that the distil end is secured in cortical bone giving the screw better purchase, however, other surgeons may prefer to avoid placing a screw so that it projects beyond the outer surface of the anchoring bone. These factors are complicated by the relative lack of soft tissue and the presence of ligaments and tendons in the small bone areas. Consequently, the less forgiving biological environment in which the small bone surgeon works requires greater procedural precision and calls for specialized implants and tools.
The present invention is designed to meet the specific needs of the small bone surgeon to facilitate effective and repeatable procedures which provide for ease of use and a range of function for this specific area of specialization. The present invention is specifically intended to provide for the treatment of fracture repair following trauma in an otherwise healthy individual where plates are used to maintain the integrity of the bones while they heal, although it is certainly possible that they may also be used for other surgeries such as reconstruction to correct congenital or age related deformation.
The plate is designed specifically for use on the lateral aspect of the fibula, and in particular for the repair of TYPE B, transsyndesmotic fractures. These fractures typically occur when the foot is subjected to axial loading and is in supination, such as can happen during a skiing accident. The talus rotates externally and the fibula fails which results in an oblique fracture beginning at the ankle joint and extending proximally from anterior to posterior. The fracture often also includes fracture of the posterior malleolus or injury of the syndesmotic ligament, and in more extreme cases with a medial failure marked by a rupture of the deltoid ligament of a transverse fracture of the medial malleolus.
The present invention provides a plate with bilaterally asymmetry (meaning that the left half of the plate is not exactly the same as the right half of the plate taken from the medial axis) and with bi-planar screw fixation (meaning that the screws do not lie in a single plane) and further which is designed to facilitate three dimensional contouring to accommodate individual variation in bone shape. The plate is configured to bend laterally, longitudinally, and to wrap or spiral about its longitudinal axis so that it can be molded to an optimal shape for small bone procedures. The plate is designed to provide optimal stabilization of fractures and osteotomies by providing multi-planar fixation that allows for better pull-out and limited axial loading to the bone. The plate is further designed to accelerate fusion success by reducing or eliminating torsional or twisting stresses to the bone segments during the healing process. In addition, when desired, the plate can be shaped so as to apply a compressive, or even a tensile, force, for example, along the longitudinal axis of a bone.
The plate is provided in a number of variations in a surgical tray, for example which include various lengths of the central trunk portion and the number of screw holes in the trunk. This allows the surgeon to select a plate during surgery after opening the wound area and considering the plating needs.
The plate has an elongate central trunk portion including one or more screw holes separated from each other by a waist shaped linking portion along a longitudinal axis. The plate further has a set of arms including screw holes which are placed at an equal distance from the longitudinal axis but which diverge asymmetrically from the longitudinal axis to avoid conflicts in the screw placement of the paired arm, specifically, so that the screws of a set of arms avoid impinging on each other. The plate is radiused about the inferior surface, (i.e. the surface which faces toward and which may, but does not have to fully contact the bone), with a curvature corresponding generally to the curvature of a bony surface. The pair of arms continue this curvature and the through holes are placed so that the angle of the longitudinal axis of the screws converge in the direction of the distil end of the screw. The screw holes are placed with the longitudinal axis perpendicular to a tangent to the top surface of the arm with the effect that the longitudinal axes of the screws converge in the direction of the distil end. The convergence of the screw holes increases the pull-out strength of the screws.
Further the screw holes are rounded and the corresponding mating heads of the screws are rounded and have a low profile so that the screws can be seated with their longitudinal axes at a variety of angles. Preferably, there is at least 20° of conical rotation, and more preferably 25°, and most preferably 30° of conical rotation of the screw axis in relation to the longitudinal axis of the screw hole (i.e. the longitudinal axis of the screw can be rotated through a conical shape about the axis of the screw hole where the apex of the cone describes an angle of 30°). Alternatively, the screw holes can include internal threads which mate with external threads on the head of the screws to cause locking of the screws relative to the plate.
While the screws are at convergent angles, the screws typically do not in fact impinge on each other, or conflict in their placement since each of the arms of the plate in a pair form a different angle to the central trunk so that the longitudinal axis of the screws are offset from each other along the length of the plate. The radiused configuration of the plate is designed to increase operating room efficiency by facilitating commonly desirable shapes while maintaining the required strength and by permitting bending without deforming the screw holes. This results in making customization in anticipation or during surgery easier.
The screws useful with the plate of the present invention are self-starting, self-tapping screws including the option of partial or full cannulation. The screws include a unique cutting end having multiple flutes, and preferably 2 or 3 flutes about a conical recess. The screws further include a partial taper of the inner diameter in the proximal end over the first several thread turns, for example over 2-8, and preferably over 3-5 turns in order to increase the fatigue life of the screw as well as providing potential physiological advantages in use. The screws further include a torque driving recess that may be a hexagon, a torx shape, or a modification of a torx shape, i.e. a multilobe shape having from 3 to 12 lobes, and preferably having 4 to 8 rounded recesses or lobes. The recess can be of a constant size in the direction of the longitudinal axis, or can taper inward along the longitudinal axis of the screw toward the bottom of the recess. The screws have a low profile, head which is rounded at the junction of the head and the shaft, and also rounded from the maximum diameter toward the top surface or the proximal end relative to the insertion tip, which includes the torque driving recess. This rounded low profile head keeps the screw from having any sharp projecting edges which could provide an irritation to the tissue in the vicinity of the plate and further seats in the plate so that no more than 10% by volume of the screw head projects from the plate.
The instruments for use with the system are well-balanced and ergonomically designed with sufficiently long handles to place the surgeon's hands outside of the line of radiation and designed to reduce fatigue in the operating room.
The plate system of the present invention is thus designed to fit a range of needs of the surgeon operating on the small bones to allow him or her to perfect a variety of techniques using a set of instruments and a customizable plate and screw construct.